With increasing popularity of mobile voice and data communication, there is an ever increasing demand for high-speed voice and data communication. The licensed spectrum for cellular communication is rapidly being exhausted by a dense and growing subscriber base. This applies in particular to the valuable low-frequency bands with low propagation loss traits.
A significant amount of unlicensed spectrum is available. For illustration, a significant amount of spectrum is globally available in the 5 GHz band. It is desirable to utilize the LTE-unlicensed (LTE-U) spectrum to augment the capacity of licensed frequency carriers. The LTE-U spectrum may be used for carrying data traffic for mobile services. The purpose of LTE-U is to extend LTE cellular communication to unlicensed spectrum.
Because the spectrum in the unlicensed band may also be used by communication techniques different from cellular communication, a communication device, e.g. an eNodeB, will not always be able to transmit when it intends to transmit LTE-U data. The reason for this is that radio resources in the LTE-U spectrum may be used by Wi-Fi or other non-cellular communication techniques.